1. Field of the Invention
The present invention relates to and image erasing method and an image erasing apparatus capable of erasing an image, which has been recorded on a thermoreversible recording medium, by converting beams emitted from a semiconductor laser (LD) array in which a plurality of semiconductor lasers (LD) are linearly aligned to a linear beam having a high uniformity through an optical lens, and applying the linear beam to the thermoreversible recording medium.
2. Description of the Related Art
Each image has been so far recorded and erased on a thermoreversible recording medium (hereinafter, may be referred to as “recording medium” or “medium”) by a contact method in which the thermoreversible recording medium is heated by making contact with a heat source. For the heat source, in the case of image recording, a thermal head is generally used, and in the case of image erasing, a heat roller, a ceramic heater or the like is generally used.
Such a contact image processing method has advantages in that when a thermoreversible recording medium is composed of a flexible material such as film and paper, an image can be uniformly recorded and erased by evenly pressing a heat source against the thermoreversible recording medium with use of a platen, and an image recording apparatus and an image erasing apparatus can be produced at cheap cost by using components of a conventional thermosensitive printer. However, when a thermoreversible recording medium incorporates an RF-ID tag as described in Japanese Patent Application Laid-Open (JP-A) No. 2004-265247 and Japanese Patent (JP-B) No. 3998193, the thickness of the thermoreversible recording medium is thickened and the flexibility thereof is degraded. Therefore, to uniformly press a heat source against the thermoreversible recording medium, it needs a high-pressure. Moreover, in the contact type, a surface of the recording medium is scraped due to repetitive recording and erasure and irregularity is formed thereon, and some parts are not in contact with a heating source such as a thermal head or hot stamping. Thus, the recording medium may not be uniformly heated, causing decrease of image density or erasure failure (Japanese Patent (JP-B) No. 3161199 and Japanese Patent Application Laid-Open (JP-A) No. 09-30118).
In view of the fact that RF-ID tag enables reading and rewriting of memory information from some distance away from a thermoreversible recording medium in a non-contact manner, a demand arises for thermoreversible recording media as well. The demand is that an image be rewritten on such a thermoreversible recording medium from some distance away from the thermoreversible recording medium. To respond to the demand, a method using a laser is proposed as a method of recording and erasing each image on a thermoreversible recording medium from some distance away from the thermoreversible recording medium when there are irregularities on the surface thereof (see JP-A No. 2000-136022). It is the method by which non-contact recording is performed by using thermoreversible recording media on shipping containers used for physical distribution lines. Writing is performed by using a laser and erasing is performed by using a hot air, heated water, infrared heater, etc.
As such a recording method using a laser, a recording device (laser maker) is proposed of which a thermoreversible recording medium is irradiated with a high output laser beam, and the irradiated position can be controlled. A thermoreversible recording medium is irradiated with a laser beam using the laser marker, and a photothermal conversion material in the recording medium absorbs light so as to convert it into heat, which can record and erase the image. An image recording and erasing method using a laser has been proposed, wherein a recording medium including a leuco dye, a reversible developer and various photothermal conversion materials in combination is used, and recording is performed thereon using a near infrared laser beam (see, JP-A No. 11-151856).
As a method for recording on a rewritable thermoreversible recording medium using a near-infrared laser beam, for example, there is a method in which non-contact rewriting is performed using laser beams emitted from a semiconductor laser (LD) light source.
In a laser recording apparatus (laser marker) performing non-contact rewriting using a semiconductor laser, a small circular beam of high output is necessary to print small words with a thin line at high speed. Thus, as shown in FIG. 1, in order to convert linear beams emitted from a LD array 1 including a plurality of LD light sources to a circular beam, a fiber coupled LD constituted with a special optical lens system 11, a optical fiber 12, and the like is used. However, the larger the number of the LD array light sources becomes for higher output of the laser beam, the more complicated the special optical lens system 11 is. Thus, a cost for an apparatus increases. Moreover, in the fiber coupled LD, the lens system is mounted so that the LD light sources cannot be cooled directly. Therefore, the fiber coupled LD has poor cooling efficiency, and difficulty in increasing output. In addition, the fiber coupled LD is a complicated optical system, and thus all laser beams cannot enter the fiber, causing decrease in efficiency, and difficulty in increasing output.
In the case of image recording, a portion where an image is recorded is irradiated with a laser beam by a vector method, while in the case of image erasing, a thermoreversible recording medium is entirely irradiated with a laser beam. In order to perform image erasing at high speed, it is necessary to increase the out put of the laser beam.
As an image erasing method using the laser recording apparatus, as shown in FIGS. 2A to 2D, proposed is an image erasing method in which scanning is performed by superimposing in parallel circular beams emitted from a typical laser marker (see Japanese Patent (JP-B) No. 4263228, Japanese Patent Application (JP-A) Nos. 2008-62506 and 2008-213439).
However, these proposed methods have such a problem that a cost for an apparatus is high for increasing the output of a laser beam.
In order to increase the output of a LD light source, a LD element (LD array) including a plurality of LD light sources is generally used, since the LD light source may be broken when the output of the LD light source formed of a single light source is drastically increased. For example, a laser beam heating tool is proposed in JP-B No. 3256090. In the proposed laser beam heating tool, laser beams emitted from a LD array 1 in which a plurality of light sources are linearly aligned, is converted to a strip-shaped beam using a first cylindrical lens 13 as shown in FIG. 3. In FIG. 3, 14 denotes a second cylindrical lens for focusing a parallel strip-shaped beams emitted from a first cylindrical lens 13 in a width direction. However, this proposal does not clearly specify whether or not the strip-shaped beam emitted from the first cylindrical lens 13 is uniform, and beams are focused through the second cylindrical lens 14 so as to perform soldering and correction of soldering. This proposal has different structure and object from those of the present invention.
An image recording and erasing are proposed in JP-A No. 2008-137243. Here, an image recording and erasing is performed on a thermoreversible recording medium using a line light source in which an imaging lens is provided to each light source of a LD array, and the LD array includes a plurality of light sources which are aligned so as to form a strip-shaped beam having uniform light distribution.
However, in this proposal, since the imaging lens is provided with respect to each of the light sources of the LD array, the apparatus has a complicated structure. The width of the light source of the LD array and the width of the irradiated beam on a thermoreversible recording medium are the same. It is necessary to broaden the width of the LD array light source. As a result, there are such problems that the apparatus size becomes large, and a cost for the apparatus outstandingly increases.
Moreover, JP-A Nos. 10-92729 and 2002-353090 discloses a lighting unit in which an optical lens is mounted so as to form a uniform light distribution. However, JP-A Nos. 10-92729 and 2002-353090 do not disclose nor suggest that image recording and erasing are repeatedly performed on a rewritable thermoreversible recording medium by irradiating it with a near-infrared laser beam.
Therefore, currently, there is a demand for promptly providing an image erasing apparatus and an image erasing method capable of performing erasure at high speed with low energy, and outstandingly decreasing a cost for an apparatus.